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SubjectRe: bpfilter logging write errors in dmesg
On Mon, Jul 27, 2020 at 03:28:55PM +0200, Christoph Hellwig wrote:
> On Mon, Jul 27, 2020 at 12:46:36PM +0200, Christian Brauner wrote:
> > Hey Christoph,
> >
> > Seems that commit
> > 6955a76fbcd5 ("bpfilter: switch to kernel_write")
> > causes bpfilter to spew these useless messages in dmesg?
> >
> > [ 26.356824] Started bpfilter
> > [ 26.357059] bpfilter: write fail -22
> > [ 26.396244] Started bpfilter
> > [ 26.396325] bpfilter: Loaded bpfilter_umh pid 637
> > [ 26.396542] bpfilter: write fail -22
> > [ 26.409588] bpfilter: Loaded bpfilter_umh pid 638
> > [ 26.410790] Started bpfilter
> > [ 26.410960] bpfilter: write fail -22
> > [ 26.445718] Started bpfilter
> > [ 26.445799] bpfilter: Loaded bpfilter_umh pid 640
> > [ 26.445983] bpfilter: write fail -22
> > [ 26.451122] bpfilter: read fail 0
> > [ 26.496497] bpfilter: Loaded bpfilter_umh pid 648
> > [ 26.497889] Started bpfilter
> > [ 26.750028] bpfilter: write fail -22
> > [ 26.768400] Started bpfilter
> > [ 26.768496] bpfilter: Loaded bpfilter_umh pid 661
> > [ 26.768699] bpfilter: write fail -22
> > [ 26.806550] Started bpfilter
> > [ 26.806616] bpfilter: Loaded bpfilter_umh pid 663
> > [ 26.864708] bpfilter: write fail -22
> > [ 26.872345] bpfilter: Loaded bpfilter_umh pid 666
> > [ 26.873072] Started bpfilter
> > [ 26.873194] bpfilter: write fail -22
> > [ 27.295514] kauditd_printk_skb: 22 callbacks suppressed
> >
> > This is on a pure v5.8-rc7 via make bindep-pkg. I'm not using bpfilter
> > in any shape or form afaict and haven't seen those messages before and
> > this seems to be the last change I see.
>
> I don't see any of those on 5.8-rc, just:
>
> root@testvm:~# dmesg | grep bpf
> [ 6.692550] bpfilter: Loaded bpfilter_umh pid 1849

Hm, odd

>
> That debug patch below should help to pintpoint what is going on for
> you:

Thanks for the debug patch! Applied and ran a kernel and I'm getting:

[ 21.919851] bpfilter: Loaded bpfilter_umh pid 619
[ 22.000229] rw_verify_area
[ 22.000235] bpfilter: write fail -22
[ 22.014686] Started bpfilter

I'm also seeing some other failures later:

[ 236.898220] bpfilter: write fail -22
[ 236.899255] bpfilter: write fail -32
[ 236.922557] bpfilter: Loaded bpfilter_umh pid 1101
[ 236.923310] Started bpfilter
[ 236.923521] rw_verify_area
[ 236.923524] bpfilter: write fail -22
[ 236.925273] bpfilter: read fail 0
[ 236.945117] bpfilter: Loaded bpfilter_umh pid 1103
[ 236.945925] Started bpfilter
[ 236.946123] rw_verify_area
[ 236.946126] bpfilter: write fail -22
[ 236.947641] bpfilter: read fail 0
[ 236.968143] bpfilter: Loaded bpfilter_umh pid 1105
[ 236.968734] Started bpfilter
[ 236.987777] rw_verify_area
[ 236.987781] bpfilter: write fail -22
[ 236.990072] bpfilter: read fail 0

Seems I can trigger this via iptables:

[ 437.922719] bpfilter: write fail -22
[ 437.924488] bpfilter: read fail 0
root@g1-vm:~# iptables -S
iptables v1.8.4 (legacy): can't initialize iptables table `filter': Bad address
Perhaps iptables or your kernel needs to be upgraded.

I have
CONFIG_IP_NF_IPTABLES=m
CONFIG_IP6_NF_IPTABLES=m
maybe I'm just missing another kernel option or something and I have no
idea how this bpfilter thing and iptables relate to each other. So maybe
it's not worth the effort and it's just my setup being broken somehow.

Christian

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